Multielectrode

ABSTRACT

A process is provided for manufacturing a multielectrode that may be used to record a bioelectrical potential difference at a detection site. The manufacturing process may comprise manufacturing a carrier from multiple thin layers of an insulating material. The manufacturing process may further comprise providing at least one recording electrode of a set of electrode pairs on at least one of the layers of the carrier. Each recording pair may include one active electrode surface and a different reference electrode surface. Also, the manufacturing process may further comprise folding, fastening, and gluing the layers of the insulating material to one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/595,418filed Apr. 17, 2006. The disclosure of which is incorporated in itsentirety by reference herein.

BACKGROUND

1. Field

Embodiments of the present invention relate to a multielectrode forrecording low amplitude signals originating from bioelectrical potentialdifferences, to a method of processing signals recorded by the inventedmultielectrode, to a system for recording and amplifying low amplitudebioelectrical signals, whereby an improved signal-to-noise ratio can beachieved, and to a process for manufacturing the inventedmultielectrode.

2. Background Art

In examinations recording bioelectrical signals, such as in ECG(electrocardiography), EMG (electromyography) and ENeG(electroneurography), the bioelectrical signals are detected andrecorded by electrodes. One recording electrode, especially used inENeG, comprises e.g. two large chlorinated silver plates or two halfspherical metal surfaces, e.g. of silver, applied to a patient, in thevicinity of a nerve. The size and shape of the two electricallyconducting surfaces of the electrode depend on the individualapplication and design, the distance between them is normally fixed,e.g. to 20-30 mm, and they may be enclosed in a plastic mould. Pieces offelt material soaked in saline or some other electrically conductingliquid are positioned in the recesses holding the electrode surfaces inorder to establish contact between the electrode surfaces and the skin.

The electrically conducting surfaces constituting the electrode may alsobe mounted individually, directly on the skin in appropriate individualpositions by using adhesive tape. When recording small amplitude signalsfrom a peripheral limb nerve, the electrodes are positioned and fixed tothe skin overlying the nerve, for example by adhesive tape or a Velcrostrap attached around the electrode and the limb. The recordingelectrode is preferably attached to the skin with the two electricallyconducting recording surfaces positioned directly above and along thenerve, minimizing the distance between the recording surfaces and thenerve.

A very high amplification is necessary in the recording system, sincethe amplitude of the neural signals derived from normal human limbnerves is low, between 100 and 5 microvolt. By superimposing repeatedresponses or by using an averaging procedure, an improvement of thesignal-to-noise ratio of successively recorded nerve responses can beachieved, such that the limit for discrimination of reliable responsesis around 1 microvolt.

However, there are several drawbacks with these electrodes. Due to thelow amplitude of the nerve signals, the accuracy of the recording iseasily disturbed. The recording procedure may have to be repeated whenother simultaneously recorded potentials interfere due to e.g. sweatingand movements of the patient, or when concurrent 50 Hz-disturbancesoccur. Since an averaging procedure is utilized, the intermittentelectrical stimulation used to induce the neural activity can beprolonged, thereby causing further discomfort to the patient.

Another available technique uses near nerve recording by needlemacroelectrodes. A needle macroelectrode is a needle electrode with arelatively large recording area at the tip, which is insertedpercutaneously (through the skin) and brought close to or in outercontact with the nerve. A reference electrode is positionedsubcutaneously nearby. Since the needle tip is located close to theactivated nerve fibres in near nerve recording, thesignal-to-noise-ratio is improved. In combination with averagingprocedures, discrimination of signals with an amplitude of only 0.5-0.2microvolt is possible.

In microneurography, which is another recording technique, a solidtungsten microelectrode or a concentric electrode with an outer diameterof only 200 micrometers is inserted percutaneously and positionedintraneurally. The very small surface of the active recording electrodeis brought in intimate contact with nerve fibres within an individualnerve fascicle, while the reference electrode surface is positionednearby, thereby permitting the recording of an electroneurogram ofelectrically induced nerve responses derived from the entire nerve fibrespectrum, i.e. from both thick and thin myelinated fibres and from thin,unmyelinated fibres, having diameters between 20-1 micrometers andconduction velocities between 70-1 msec. This is the only technique inman that also allows recording from single myelinated and unmyelinatednerve fibres in response to various natural stimuli applied within theinnervation area of the impaled fascicle.

However, these procedures, using sterilized needle electrodes, aretechnically very demanding, time consuming and manually difficult toexecute. They are, therefore, unsuitable as clinically routinediagnostic tools.

Related art is also described e.g. in U.S. Pat. No. 5,976,094.

The closest prior art is revealed in U.S. Pat. No. 5,660,177, disclosinga bioelectrical sensing electrode comprising an array of electrodes, bywhich the DC-potential can be recorded at several different detectionsites on a patient, in order to screen e.g. a breast, (see e.g. FIG. 1and column 5, lines 32-60). Prior art is also disclosed in US2003/009096, which describes a sensor system for measuring bioelectricalpotentials on different detection sites on the head of a patient, byusing an array of three electrodes. In all techniques described in theseprior art documents, the biological signal of interest is recorded onlyone time at the detection site. By contrast, embodiments of thisinvention provide for an improved recording of bioelectrical potentialdifferences derived from the same bioelectrical impulse generator/s/,e.g. nerve fibre/s/ or muscle fibre/s/ at only one detection site, withimproved signal-to-noise ratio achieved by using multiple recordings anda summation of the bioelectrical potential differences derived from saidimpulse generators at this detection site, using several recordingpairs, which are provided on one electrode.

An object of embodiments of this invention is to limit or eliminate someof the described problems when recording low amplitude bioelectricsignals and to provide an improved non-invasive recording electrode anda novel procedure to process the recorded signals, whereby in particularthe signal-to-noise ratio of the signals is improved compared to priortechniques, making embodiments of the invention suitable for clinicalexaminations of patients.

SUMMARY

The above object is achieved by the multielectrode, by the recordingmethod, by the recording system and by the manufacturing processaccording to the attached claims, which are hereby incorporated in theirentirety.

The claims are directed to a multielectrode comprising a carrierprovided with separate electrode surfaces for improved recording of thebioelectrical potential difference/s/ at one detection site. Saidseparate electrode surfaces include one or more active electrodesurfaces and two or more reference electrode surfaces for providing twoor more recording pairs, each of said active electrode surfacesparticipating in more than one of said recording pairs for recordingsaid bioelectrical potential difference/s/ multiple times at the samedetection site. The recording pairs are adapted to be connected toprocessing apparatus comprising inversion apparatus and summationapparatus to provide an improved signal-to-noise ratio of said recordedpotential difference/s/.

The active electrode surfaces may be centrally positioned on the surfacearea of the carrier and the reference electrode surfaces may besymmetrically positioned between the active electrode surfaces and theedge delimiting the surface area of the carrier.

The carrier may consist of two or more separate sub-carriers, of whicheach sub-carrier is provided with at least one separate electrodesurface, the total number of electrode surface being at least three.

The active electrode surfaces may all have a substantially similar sizeand shape and the reference electrode surfaces may also have asubstantially similar size and shape. The size and/or shape of thereference electrode surfaces may be substantially similar to orsubstantially different from the size and/or shape of the activeelectrode surfaces. The surface of the carrier may be provided withelevated parts to which electrode surfaces are attached, or withrecesses into which electrode surfaces are fitted, and the electrodesurfaces may extend on the sides of the elevated parts or of therecesses in the carrier.

The recesses in the carrier may be delimited by vertical edges elevatedfrom the surface of the carrier, thereby preventing short-circuitingbetween adjacent electrode surfaces.

Electrically conducting material may be attached to at least some of theelectrode surfaces.

The carrier and/or the electrode surfaces may be provided with anadhesive for attaching the multielectrode to the detection site.

The carrier with the electrode surfaces may be formed by one or morethin layer/s/of an insulating material provided with a pattern ofelectrode surfaces.

The carrier may be provided with three or more sterilized needles, ofwhich each needle tip constitutes at least part of an electrode surface.

The claims are also directed to a method of processing signalsindicating bioelectrical potential differences at a detection site, thesignals recorded by the multielectrode according to the invention, themethod comprising a summation of the signals recorded at the detectionsite by at least two recording pairs, said signals derived fromgenerators of bioelectrical potential differences.

An inversion of at least one of the signals may be performed prior tothe summation.

A delay from the starting point of the induced response may be performedbefore the summation, and at least part of one or more signals may bemuted prior to the summation.

The claims are also directed to a process of manufacturing saidmultielectrode, at least part of the process being manual, or at leastpart of the process being performed by mechanical manufacturingapparatus. The steps may comprise the manufacturing of thin layers of aninsulating material, providing some of the layers with patterns ofelectrode surfaces and folding, fastening and/or gluing the layerstogether.

The claims also relate to a system for recording signals indicatingbioelectrical potential differences at a detection site, the systemcomprising at least one multielectrode and processing apparatusconnected to said multielectrodes, the processing apparatus comprisingsummation apparatus and inversion apparatus.

The processing apparatus may further comprise delay apparatus and mutingapparatus.

Other features and further advantages of the invention will be apparentfrom the following description and the described nonlimiting embodimentsof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described in more detailand with reference to the drawings, of which:

FIG. 1 illustrates a top view of a presently used macroelectrode,

FIG. 2 illustrates an arrangement for recording electrically evokedneural activity;

FIG. 3 is a top view of a first embodiment of the inventedmultielectrode;

FIG. 4 is a perspective view of a second embodiment of the inventedmultielectrode;

FIG. 5 is a perspective view of a fourth embodiment of the inventedmultielectrode; and

FIG. 6 is a block diagram illustrating one method of processingbioelectric signals recorded by the invented multielectrode.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

One object of embodiments of the invention is to improve the recordingof low amplitude bioelectric signals originating from generators ofbioelectrical potential differences, i.e. from nerve fibers or motorunits. This is accomplished by the invented electrode, comprising aplurality of separate recording surfaces, by the invented processingmethod, by the invented system and by the invented manufacturingprocess.

FIG. 1 illustrates one prior art macroelectrode 1, provided with twoelectrode surfaces 2 a and 2 b of an electrically conducting material,preferably a metallic material. The size of the prior art macroelectrodeis approximately 1 cm×2.5 cm×5 cm, and the size of each of the twoelectrode surfaces is approximately 6 mm×20 mm. The macroelectrode isintended to be fixed to the skin overlying a nerve with the electrodesurfaces facing the skin.

FIG. 2 schematically illustrates an arrangement for recording neuralactivity in a large number of nerve fibers located in a peripheral nerveat the wrist of a patient. In this arrangement, the bioelectric neuralactivity is evoked by repetitive electrical shocks applied to thepatient at a stimulation site 3 located on one of the patient's fingers.However, bioelectrical activity may alternatively be evoked by magnetic,physical or natural stimulation, such as e.g. by skin stimulation and,in other arrangements, by voluntary muscle contractions, light flashesor sounds. A bioelectrical signal between two spots on the skin of thepatient, caused by the evoked neural activity, is detected by arecording electrode attached to the patient at a detection site 4located on the wrist of said patient. The arrangement is furtherprovided with appropriate electrical grounding apparatus, which is notillustrated in this figure. The signals recorded by the electrode areprocessed electronically in order to obtain an optimal signal to bedisplayed, e.g. on an oscilloscope.

When recording bioelectrical signals in an animal, the detection sitemay be on the skin of the animal, or alternatively in a paraffin filledpool limited by skin flaps where the electrode surfaces are submerged tocontact a nerve or some other generator of bioelectrical potentialdifferences in the animal, e.g. a nerve root. The electrode surfaces inthe pool may be located in intimacy or close to the top or underneathsaid generator.

In order to improve the signal-to-noise-ratio of recorded bioelectricalpotential differences at a detection site, which e.g. is located on theskin directly overlying a nerve of a patient, the novel electrodeaccording to embodiments of this invention comprises a carrier providedwith a plurality of separate electrode surfaces. The electrode surfacesinclude one or more active electrode surfaces to be attached to the skinat a central part of the detection site, and two or more referenceelectrode surfaces to be attached to the skin at a small distance fromthe center of the detection site. The active electrode surfaces arepreferably centrally positioned on the electrode carrier and thereference electrode surfaces are preferably positioned between theactive electrode surfaces and the edge of the surface area of thecarrier, the localization depending on the shape and size of thecarrier. The reference electrode surfaces may be grouped, so that thegroups located on the carrier symmetrically surround the activeelectrode surface or surfaces.

The recording of a potential difference, i.e. a bioelectrical signal, isachieved by pairs of electrode surfaces, one active (negative) and onereference (positive) electrode surface, constituting one recording pairbetween which the potential difference is detected. By using multipleelectrode surfaces, the bioelectrical potential difference/s/occurringat one detection site can be detected multiple times, by severalrecording pairs at this site, with the active electrode surface/s/participating in more than one recording pair. However, the presentdisclosure further contemplates that the bioelectrical potentialdifference/s/ occurring at one detection site may be determined multipletimes using at least one active electrode surface and at least onereference electrode surface. The present disclosure further contemplatesthat the bioelectrical potential difference/s/occurring at one detectionsite may be detected multiple times using at least one active electrodesurface and a first and second reference electrode surface. Processingapparatus connected to the multielectrode, including an inversion and asummation unit, adds the recorded values of the bioelectrical potentialdifferences detected by each recording pair, of which at least one ofthe values may be inverted before summation, thereby achieving animproved recording of the bioelectrical signal, i.e. regarding thesignal-to-noise-ratio.

The number of active electrode surfaces provided on a multielectrode isone or more and typically between one and three. The number of referenceelectrode surfaces is two or more and typically between four and twenty.

The electrode surfaces of one multielectrode may have different shapesand sizes.

However, if the electrode surfaces have similar shape and size, theirelectrical impedance is similar, which may be advantageous. According toone embodiment of the invention, all of the active electrode surfaces ofone multielectrode have similar shape and size and all of the referenceelectrode surfaces have similar shape and size, while the size and shapeof the reference electrode surfaces is different from the shape and sizeof the active electrode surfaces, or, alternatively, only the shape isdifferent while the size of all of the electrode surfaces is similar.

FIGS. 3-5 show top views of exemplary embodiments of the inventedmultielectrode, provided with a multitude of separate electrodesurfaces. The potential difference at a detection site is detected andmeasured by several recording pairs, each recording pair consisting ofone of the active electrode surfaces and one of the reference electrodesurfaces of the multielectrode. The recorded values are processed andsummed, achieving an improved recording of a bioelectrical signal.

FIG. 3 illustrates a first embodiment of the invented multielectrode 5,having a rectangular electrode carrier 8, on which rectangular electrodesurfaces are attached. The electrode, according to this exemplaryembodiment, is provided with one group 6 of two active electrodesurfaces, and with two groups, 7 a and 7 b, each with three referenceelectrode surfaces, the two groups positioned on either side of thegroup of active electrode surfaces 6. The multielectrode is intended tobe applied to a patient with the active electrode surfaces locateddirectly overlying the detection site, e.g. in a nerve of a patient. Ifthe rectangular electrode carrier is positioned along the stretch of thenerve, the stretch of an individual, rectangular, electrode surface isperpendicular to the longitudinal stretch of the nerve.

FIG. 4 illustrates a second embodiment of the invented multielectrode 5,having a more quadratic configuration of the electrode carrier 8, towhich separate electrode surfaces are attached. The multielectrodeaccording to this second, exemplary, embodiment is provided with onegroup, 6, of three substantially quadratic active electrode surfaces andwith two groups, 7 a, 7 b, each with five rectangular referenceelectrodes. In this embodiment, the three groups of electrode surfacesare located in parallel on the carrier, the group of active electrodesurfaces located in between the two groups of reference electrodesurfaces and intended to be located directly above the stretch of thenerve.

According to a third, not illustrated, embodiment of the inventedmultielectrode, the configuration of the multielectrode carrier 8comprises two or more separate sub-carriers, intended to be individuallyapplied to the detection site 4 of a patient. Each sub-carrier isprovided with one or more separate electrode surfaces, of which theactive electrode surfaces preferably are positioned on the samesub-carrier. The total number of electrode surfaces must be three ormore.

FIG. 5 illustrates a fourth, exemplary embodiment of the inventedmultielectrode 5, having a circular electrode carrier 8, on theelevations of which separate electrode surfaces are attached. Themultielectrode is provided with only one, centrally located, activeelectrode surface 6 and four groups, 7 a, 7 b, 7 c, 7 d, of referenceelectrode surfaces, each with three reference electrodes, these fourgroups surrounding the active electrode surface and positioned withapproximately 90 degrees angular distance from each other. The carriersurface of this embodiment may have e.g. a circular, semicircular,semiellipsoid, partly rectangular or partly square extension. Accordingto an alternative embodiment, the electrode surfaces are attached intorecesses in this type of electrode carrier.

A multielectrode according to FIG. 5 is mainly intended for recording ofsignals in a detection site from which signals are spread uniformly,which occurs e.g. when obtaining precordial leads of ECG-recordings orin surface EMG-recording.

The size of the carrier of the invented multielectrode may varyconsiderably depending on the application of the multielectrode, but arectangular carrier, according to the embodiment illustrated in FIG. 3,may have an approximate length of e.g. 5 cm, a width of e.g. 2.5-3.5 cmand a thickness of e.g. 1-1.5 cm. The electrode surfaces may be attachedin the bottom of recesses in the carrier, the recess having a depth ofe.g. 10 mm, a length of e.g. 20 mm and a width of e.g. 2-4 mm. Theelectrode surfaces may extend on the sides of the recess. Alternatively,the electrode surfaces may be attached, e.g. glued, on elevated parts ofthe surface of the carrier, the elevated parts having a height ofapproximately up to 10-15 mm, a length of e.g. 10 mm and a width of e.g.1.5 mm. The electrode surfaces may extend on the sides of the elevatedparts.

Part of an electrode surface may be unexposed due to insulating materialcovering part of the surface.

The individual size of an exposed or unexposed electrode surface dependson the application, but is typically between 40-150 mm2. However, theelectrode surface may be as small as a few mm2 and larger than 200 mm2.

By extending the electrode surfaces on the side of recesses or onelevated parts of a carrier, a larger electrode surface area ispossible, whereby e.g. a lower impedance can be achieved.

The distance between adjacent electrode surfaces, i.e. theinterelectrode distance, may vary according to the application, the sizeof the carrier and the size and shape of the electrode surfaces, but maytypically be between 1 mm and 2 mm. However, by varying theinterelectrode distance, various degrees of packing and/or grouping ofactive and of reference electrode surfaces can be achieved.

The distance between the electrode surfaces of one recording pairdepends e.g. on the size of the electrode carrier and the location ofthe reference electrodes in relation to the active electrodes. It isnormally between 12 mm and 20 mm, but may be shorter or longer. Thevariations in the distances between the electrode surfaces constitutingthe recording electrode pairs on one multielectrode is, however,preferably less than 5 mm.

Electrically conducting material, such as e.g. a gel or a moistabsorbing fabric or felt soaked in e.g. saline, may be attached to theelectrode surfaces in order to establish the contact between theelectrode surface and the skin. The attachment may be achieved e.g. bypressing the electrically conducting material into recesses or wrappingit around elevations and holding it in place by plastic pieces or byappropriately adopted o-rings.

The carrier and/or the electrode surfaces may be provided with anadhesive in order to secure the attachment of the electrode to the skinof the patient.

The electrode surfaces are electrically insulated from each other byplastic, mould or by air, and are individually connected to shieldedconductors within a cable, which feeds the obtained signals from arecording pair individually into the processing apparatus.

Recesses in the carrier may be delimited by thin, vertical edgeselevated from the horizontal surface of the carrier, thereby preventingshort-circuiting between neighboring electrode surfaces placed in saidrecesses.

According to another embodiment of the invented multielectrode, themultielectrode is manufactured in a thin version, as a stick-onelectrode, adapted to be fastened to the skin of a patient with adhesivetape. For example, with reference back to FIG. 3, the multielectrode 5may be manufactured so that the carrier 8 may be formed by one or morethin layer/s/ of mould of semi-elastic plastic. The multielectrode 5 mayfurther be formed so that various patterns of active and passiveelectrode surfaces 6, 7 a, and 7 b, may be positioned within carrier 8so that each electrode surface is electrically separated by theinsulating layers. Although FIG. 3 illustrates the active and passiveelectrode surfaces 6, 7 a, and 7 b substantially within the edges of thecarrier 8, the present disclosure contemplates that at least a portionof the active and passive electrodes 6, 7 a, and 7 b may extend beyondthe edges of the carrier 8. By cutting and/or folding the one or morecarrier 8 layer/s/ and gluing them together, flat multielectrodes ofdifferent design may be achieved.

According to another embodiment of the invented multielectrode, thecarrier is provided with three or more needles of which the needle tipconstitutes an electrode surface, or part of an electrode surface. Sucha sterilized multielectrode is adapted to penetrate the skin of apatient. For example, with reference to FIG. 4, the reference electrodes7 a, 7 b and the active electrodes 6 are elevated away from the carrier8. One or more of the elevated active and reference electrodes 6, 7 a, 7b may be formed so as to include a needle tip adapted to penetrate theskin of a patient.

The signals from the recording pairs of the multielectrode are fed toprocessing apparatus, connected to the multielectrode, and summed insummation apparatus, thereby achieving the desired improvedsignal-to-noise-ratio. The recordings from different recording pairs canhave different polarity. However, a common polarity is preferablydefined in the processing apparatus and an inversion of some of therecordings is performed before the summation.

If the bioelectrical signal is evoked by repetitive electricalstimulation and recorded by a large number of recording pairs, theelectrical stimulation signal, i.e. the stimulus artifact, whichprecedes the nerve response, may cause a saturation of the summationunit, thereby distorting the recording. This can be avoided by providingdelay apparatus, whereby a canceling of the stimulus artefact can beaccomplished by inverting some recorded signals with a delay after theartefact, thus inverting only the neural response and not thecorresponding artefact. Alternatively, the parallel amplifiers connectedto the summation unit may be muted for the duration of the electricalstimulus, thereby providing muting arrangements. Also, in some casessome of the nerve responses must be inverted before summation.

FIG. 6 is a block diagram illustrating one method of processing signalsrecorded by one embodiment of the invented multielectrode 5, which isonly provided with one active electrode surface 6 and two referenceelectrode surfaces 7 a, 7 b. Bioelectrical potential differences in theskin overlying a nerve of a patient are detected and measured by tworecording pairs 9 a, 9 b, of which 9 a consists of electrode surfaces 6and 7 a and 9 b consists of electrode surfaces 6 and 7 b. The recordingpairs are connected to amplifying and filtering apparatus 10 a, 10 b,from which the output signals are fed to inverting and delayingapparatus 11 a, 11 b. The output signals from the inverting and delayingapparatus are connected to summation apparatus 12. The summed signalsare, subsequently, displayed by display apparatus 13, which may comprisee.g. a personal computer or an oscilloscope.

The multielectrode, may be manufactured by suitable e.g. mechanicalmanufacturing apparatus, and part of the manufacturing process may bemanual. A substantially flat multielectrode may be manufactured byfastening together, e.g. by glue, thin layer/s/ of very thin plastic orother insulating material, of which some of the layer/s/are providedwith various patterns of electrode surfaces.

Thus, by the described multielectrode comprising a plurality of separaterecording surfaces, by the parallel processing of the signals recordedby the multielectrode, by the system comprising the multielectrode andprocessing apparatus and by the manufacturing of these items, animproved recording of low amplitude bioelectric signals, originatingfrom bioelectrical potential differences, can be accomplished.

The invention is not restricted to the described embodiments in thefigures, but may be varied freely within the scope of the attachedclaims.

1. A process of manufacturing a multielectrode for recording abioelectrical potential difference at a detection site, the processcomprising: manufacturing a carrier from multiple thin layers of aninsulating material; providing at least one recording electrode of a setof electrode pairs on at least one of the layers of the carrier, eachrecording pair including one active electrode surface and a differentreference electrode surface; and folding, fastening, and gluing thelayers of the insulating material to one another.
 2. The process ofclaim 1 wherein at least part of the process is manual.
 3. The processof claim 2 wherein at least part of the process is performed bymechanical manufacturing apparatus.
 4. The process according to claim 1wherein thin layers are manufactured in thin layers of semi-elasticplastic.
 5. The manufacturing process of claim 1, wherein the carrier ismanufactured to include at least three sterilized needles, each needletip constituting at least a portion of each respective electrodesurface.
 6. The manufacturing process of claim 1 wherein the insulatingmaterial electrically insulates each of the respective electrodesurfaces.
 7. The manufacturing process of claim 1 wherein the size andshape of the active and reference electrode surfaces is manufactured tobe substantially similar so that the electrical impedance issubstantially similar.
 8. The manufacturing process of claim 1 whereinthe at least one active electrode surface is manufactured to besubstantially positioned in a central location on the carrier.
 9. Themanufacturing process of claim 1 wherein each reference electrodesurface is manufactured to be symmetrically positioned between theactive electrode surface and an edge delimiting the surface area of thecarrier.
 10. The manufacturing process of claim 1 wherein the size andshape of at least one of the reference electrode surfaces ismanufactured to be substantially different from the size and shape ofthe active electrode surface.
 11. The manufacturing process of claim 1wherein the carrier is manufactured to include elevated portions towhich each of the respective electrode surfaces are coupled.
 12. Themanufacturing process of claim 1 wherein at least one of the respectiveelectrode surfaces is manufactured to extend beyond the side of theelevated portion.
 13. The manufacturing process of claim 1 wherein thecarrier is manufactured to include recesses into which each of therespective electrode surfaces are fitted.
 14. The manufacturing processof claim 13 wherein at least one of the electrode surfaces ismanufactured to extend on the sides of the recesses.
 15. Themanufacturing process of claim 14 wherein each recess is delimited byvertical edges elevated from the carrier, thereby preventingshort-circuiting between adjacent electrode surfaces.
 16. Themanufacturing process of claim 1 wherein the carrier is manufactured toinclude electrically conductive material that is attached to at leastone of the electrode surfaces.
 17. The manufacturing process of claim 1wherein the carrier is manufactured to include an adhesive for attachingthe multielectrode to a detection site.